The present invention relates to receiving caller identification (CID) information with a telecommunications device for the deaf (TDD).
Wired telephones are connected to a telephone company""s central office (CO) through a two-wire circuit called a local loop. A CO contains switching equipment that connects the telephone lines of a calling telephone terminating at one CO to the telephone lines of a called telephone terminating at another CO. When the switches between a telephone and a CO are open (e.g., because a telephone handset is holding down a switchhook), there is no connection between the telephone and the CO. However, once the switches between a telephone and a CO are closed (e.g., because the telephone handset is removed, causing the switchhook to lift up), the local loop is complete, thus establishing a connection between the telephone and the CO.
When a calling telephone is connected with the calling telephone""s CO (the xe2x80x9ccalling COxe2x80x9d), it generates a signal that tells the calling CO that a person wants to make a call. The calling CO returns a dial tone to the calling telephone indicating that the calling CO is ready to accept a telephone number. The person dials a telephone number that is sent to the calling CO. The calling CO transmits the telephone number over a telephone network and connects with a called telephone""s CO (the xe2x80x9ccalled COxe2x80x9d).
The called CO then attempts to complete the call by making a final connection to the called telephone. If the called telephone is on-hook when the called CO attempts to complete the call, the called CO send a ringing signal to the called telephone to indicate that a call is waiting. At the same time, ring-back tones are sent to the calling telephone, generally by the called CO or the calling CO. Once the called telephone is off-hook, the called telephone is connected with the called CO, which sends a signal through the telephone system indicating that it is connected with the called telephone. Thus, the ringing signal to the called telephone and the ring-back tones to the calling telephone are discontinued, and the calling telephone and the called telephone are connected.
A telecommunications device for the deaf (TDD) allows hearing-impaired persons to use telephones to communicate by typing messages. Generally, a TDD contains a keyboard, a modem, a display screen and/or a printer, and special acoustic cups into which a telephone handset is placed to connect the TDD to a CO via a telephone. To use a TDD, a person takes a telephone handset off-hook and places the handset into the acoustic cups. Once a calling TDD is connected to the calling CO via the telephone, the TDD user dials the telephone number of another TDD.
The called TDD xe2x80x9cringsxe2x80x9d by a light on the TDD blinking in conjunction with the ringing signal sent to the called TDD. When the handset for the called TDD""s telephone is off-hook and placed in the called TDD""s acoustic cups, the called TDD is connected with the called CO. The called CO transmits a signal through the telephone system indicating the connection with the called TDD, ring-back tones to the calling TDD are discontinued, and the called TDD and calling TDD are connected. Some TDDs connect directly to the telephone line in the same manner as a telephone, and thus do not contain acoustic cups. These TDDs contain the circuitry, usually contained in a telephone, that completes the connection to the CO and thus do not need to hold a telephone handset.
A TDD connected with a CO, whether via a telephone whose handset is placed on a TDD""s acoustic cups, via circuitry internal to a TDD, or otherwise, is xe2x80x9coff-hook.xe2x80x9d Conversely, a TDD that is not connected to a CO is xe2x80x9con-hook.xe2x80x9d In addition, with regard to both TDDs with acoustic cups and TDDs without acoustic cups, a TDD from which a call is made is a xe2x80x9ccalling TDD,xe2x80x9d and a TDD to which the call is made is a xe2x80x9ccalled TDD.xe2x80x9d
Once the calling and called TDDs are connected with each other via their respective COs, the TDD users type messages using their TDD keyboards. The typed characters produced by the TDDs are Baudot characters that are converted into frequency shift keyed (FSK), then and transmitted over a telephone line. When the FSK tones reach the other TDD, they are converted back into Baudot characters to be displayed on the TDD""s display screen, and/or printed on the TDD""s printer. A TDD message can be transmitted and received only when the calling TDD and the called TDD are off-hook.
Caller ID (CID) is a service offered by telephone companies that provides to a called party information regarding a calling party, e.g., the telephone number of the calling telephone. CID information is sent to a CID reception device connected to the called telephone. CID information is available to TDD users by connecting a CID reception device to the TDD""s telephone (for a TDD with acoustic cups) or the TDD (for a TDD without acoustic cups). Consequently, a TDD user incurs the cost of a CID reception device, in addition to the cost of a TDD, in. order to receive CID information. A TDD cannot receive information in the same format as a CID reception device. Furthermore, CID information is transmitted to a CID reception device while the called party""s telephone is on-hook. By contrast, a TDD message is transmitted to a TDD while the TDD is off-hook.